A centralizer with low friction buttons and method of fabrication thereof

ABSTRACT

A centralizer with low friction buttons comprising a plurality of collars including a first collar and a second collar; a plurality of bow springs, each bow spring having a first end and a second end; and a plurality of low friction buttons. The plurality of bow springs extend between the first and second collar such that the first and second end of each bow spring is connected to the first and second collar respectively; the plurality of low friction buttons are mounted on the bow springs such that they act as the only point of contact between the centralizer and borehole during movement of the pipe casing while getting it to the total depth during drilling operation, said buttons being of the type whose coefficient of friction is lesser than the rest of the body of the centralizer.

FIELD OF THE INVENTION

The present invention relates to a centralizer with low friction buttons. More specifically, the present invention provides a centralizer device that has low friction buttons that are designed and placed strategically on the centralizer so as to reduce the start up torque while running down or coming up a casing.

BACKGROUND OF THE INVENTION

Correct centralization of the casing, in the wellbore, is essential for proper functioning of the well. While incorrect centralization can result in channeling and poor cementation. Centralization of casing in the well is achieved by centralizers. Centralizers are used to place the pipes and casings in the centre of the wellbore and to allow cement to circulate freely around the tube and produce a robust cement seal, ensuring the zonal isolation. Centralizers also minimize the differential sticking of the casing to the wellbore and thus equalize the hydrostatic pressure in the annulus.

If centralizers are not strong enough or if they break the consequences can be very expensive. Approximately 400 wells worldwide are affected by centralizer problems. An average cost of per well is 1.5 million and thus producing a total loss of 0.6 billion which can be avoided by installation of better and innovative centralizers.

An ideal centralizer should have maximum stand-off; ultra-high-strength; with zero weak points such as hinges, welds or mechanical interlock; with the flexibility and; restoring force suitable to absorb both axial and radial loads. It should give the lowest co-efficient of friction and should provide maximum torque reduction in open and cased hole.

Various U.S. patents disclosed variations in centralizers as described below:

U.S. Pat. No. 4,483,395 disclosed a centralizer as one-piece wire guard device composed of non-metallic material engagable with a well pipe for preventing the abrasion of the well pipe, electric wires, ropes and the like with the well casing. More specifically, the object of this invention to provide a split-ring type guard device which may be readily opened at the split to permit the guard device to be slipped over the drop pipe and fastened thereon.

U.S. Pat. No. 4,088,185 disclosed a molded plastic scraper that is molded in place on the sucker rod and as a result of shrink fitting of the material is firmly held in place thereon. Special configurations and materials particularly useful as and in both scrapers and centralizers are disclosed as well as additional unexpected advantages of such scrapers, configurations, and materials. This invention overcomes the deficiencies of the prior art and achieves its objectives by the molding of a plastic scraper in place at one or more positions on a sucker rod whereby, as a consequence of the shrinkage of the fit and swelling of the material, a frictional grip of sufficient force to hold the scraper firmly in place under normal operating conditions is obtained with no damage or induction of stress to the sucker rod. Though, it provides a specific configuration for the multifunctional use including scrapper and centralizer. The approaches to overcome frictional issues are not disclosed.

U.S. Pat. No. 5,908,072 disclosed a non-metallic centralizer for casing having a tubular, plastic sleeve adapted to fit closely about a joint of casing, said sleeve having a plurality of blades extending substantially longitudinally along an outer surface of said sleeve. The non-metallic centralizer having strength characteristics capable of withstanding the forces encountered in casing operations. The non-metallic centralizer is non-sparking for use in hazardous environments, abrasion and wears resistant, and provides protection from electrolysis between adjacent casing strings. The non-metallic centralizer is light weight, allowing increased transportation capacity at an economical cost. The frictional issues during casing operations are not focused.

U.S. Pat. No. 6,283,205 disclosed a polymeric centralizer for casing having a body adapted to fit closely about the casing, a plurality of blades extending substantially longitudinally along an outer surface of body, a slit through a blade and opposing groove to allow the centralizer to be spread apart and a fastener to pulling the slit together and tightening the centralizer about the casing. The polymeric centralizer having strength characteristics capable of withstanding the forces encountered in casing operations. The polymeric centralizer is non-sparking for use in hazardous environments, abrasion and wears resistant, and provides protection from electrolysis between adjacent casing strings. The polymeric centralizer is light weight, allowing increased transportation capacity at an economical cost and allows easy attachment to broken down or made-up piping, production string or casing and including hole or cutaways for receiving surface cabling.

While the drawbacks of present prior arts are that, most of the prior art centralizers focused on the materialistic properties, safeguarding properties, abrasion and wear resisting properties and the like. The other problems like torque loss due to high coefficient of friction, reduction in running forces due to frictional forces between the pine casing and the borehole wall remain untouched. Hence, it would be a benefit to provide attention towards such issues by providing optimized performance centralizers with reduced frictional properties during casing operations.

OBJECT OF THE INVENTION

The main object of the invention is to provide a centralizer with low friction buttons.

Yet another object of the invention is to provide a centralizer with low friction button placed and designed strategically to reduce the start up torque while placing or extracting from a casing.

Yet another object of the invention is to provide a centralizer wherein the buttons made up of metal alloy that are integrated in the centralizer to give the centralizer its robust strength.

Yet another object of the invention is to provide a centralizer wherein the buttons made up of metal alloy that are integrated in the centralizer to provide maximum retention of the buttons during expansion and contraction of the centralizer.

Yet another object of the invention is to provide a centralizer wherein the buttons made up of metal alloy that are integrated in the centralizer fabricated on the first contact points or within highly deviated portion of centralizer having radially outward protrusion, so as to act as the first point of contact on the centralizer.

Yet another object of the invention is to provide a centralizer wherein the buttons made up of metal alloy that are integrated in the centralizer fabricated on the first contact points or within highly deviated portion of centralizer having radially outward protrusion, so as to act as the first point of contact on the centralizer and reduce the start up torque while placing or extracting from a casing.

Yet another object of the invention is to provide a centralizer with minimum torque loss when the centralizer rubs against the sidewalls of the borehole.

Yet another object of the centralizer is to provide a centralizer with vastly superior torque and drag reduction due to an extremely low coefficient of friction and it can be used successfully in either open or cased-hole applications.

Yet another object of the invention is to provide a centralizer with that transmits high torque loads axially and radially, thereby enabling the drilling operation to be conducted efficiently.

SUMMARY OF THE INVENTION

In one embodiment, the centralizer comprises first collar, second collar, a plurality of bow springs connecting the collars and specially designed button. The specially designed button further comprises of metal alloy, such as stainless steel or material with similar wear properties, integrated into the centralizer, fabricated on the first contact points or within highly deviated portion of centralizer having radially outward protrusion, act as the first point of contact on the centralizer and help to reduce the wear and abrasion of the centralizer, thereby reducing the co-efficient of friction and consequently reducing the torque.

In another embodiment of the current invention, the centralizer offers minimum co-efficient of friction and maximum torque reduction by its one piece design and materials used.

In another embodiment of the current invention, the centralizer provides a novel geometry which has unique placement of buttons composed of stainless steel that offers very less co efficient of friction. The friction reducing stainless steel buttons are attached on the centralizer body. This reduces the co-efficient of friction between the centralizer and tubing.

The present invention provides a centralizer with low friction buttons. The centralizers have specially designed buttons that are fabricated on the first contact points or within highly deviated portion of centralizer having radially outward protrusion, so as to act as the first point of contact on the centralizer.

In one embodiment of the present invention one piece design is fabricated to give robust strength to the centralizer and the unique placement of buttons which can be made up of metal alloy such as stainless steel that helps to reduce the co-efficient of friction to the minimum. The buttons inserted herein are integrated in to the centralizer while fabricating, rather than being superficial attachment, this helps in retention of the buttons on sudden and vigorous expansion and contraction of the centralizer during application. The term low coefficient of friction refers to a friction coefficient that ranges from 0.10-0.15 in water based mud (WBM) and 0.05-0.10 in oil based mud (OBM).

In another embodiment of the present invention, the low friction buttons have slightly protruded shape that allows these buttons to have a minimal point of contact between centralizer and borehole (i.e., only the buttons touch the borehole and not the centralizer) the rest area constitute an ‘air gap’.

The configuration, geometry and materials used in the present invention helps to reduce the start-up torque while running of the casing; minimizes the rotational torque loses and stall out effect; and enhanced rotation due to optimized centralization.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and brief description:

FIG. 1 is a perspective view of the centralizer in accordance with the present invention.

FIG. 2 is a schematic diagram elucidating the role of low friction buttons during run in the borehole.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings and description that follow, like parts are typically marked throughout the specification and drawings with the same reference numerals, respectively. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness.

Disclosed herein is a centralizer for use either in open or cased-hole applications. The centralizer described herein may be coupled to a wellbore tubular.

Referring to FIG. 1, an example of perspective view of the centralizer 100 in accordance with the present invention is shown. As depicted, the centralizer 100 comprises first collar 101, second collar 102, a plurality of bow springs 103 connecting the collars 101, 102. Plurality of bow springs 103 further comprises a specially designed button 104 buttons made up of stainless steel or material with similar wear properties, integrated into the centralizer 100 fabricated on the first contact points or within highly deviated portion of centralizer having radially outward protrusion, so as to act as the first point of contact on the centralizer and help to reduce the wear and abrasion of the centralizer, by acting as the point of contacts and reducing the co-efficient of friction and consequently reducing the torque.

The collars 101 and 102, and the plurality of bow springs 103 may be formed from steel, a composite, or any other similar high strength material.

The centralizer 100 or its parts may be formed from one or more composite materials. A composite material comprises a heterogeneous combination of two or more components that differ in form or composition on a macroscopic scale.

In another preferred embodiment of the present invention, the stainless steel buttons are placed inside the collars as well.

Referring to FIG. 2, a low friction button 105 is mounted on the centralizer 100, fitted closely to the outer surface of the pipe casing 104. During drilling operation, the pipe casing 104 moves in the borehole 108, in order to get itself to the total depth of the borehole. During this run-in-hole (RIH) process, the low friction button 105 touches the borehole 108 wall and help to reduce the start-up torque while running of the pipe casing 104. It gives the centralizer 100 extremely low co-efficient of friction as only the low friction button 105 contact the hole and no part of bow spring is in touch with the borehole 108. Thus, an air cushion is formed between the bow springs and the borehole 108. In such a way, the low friction button 105, reduce drag during RIH.

The centralizer 100 is able to get pipe down through tangent and build sections where the friction forces are greatest due to side loading. The low friction button make the lowering and running of pipe casing 104 extremely easy.

The holes are punched in the centralizer sheet wherein the holes are preferably oval with transverse diameter in range of 11-17 mm and longitudinal diameter in range of 13-15 mm. More particularly, the holes are punched with profile 13.5-14.5 mm/11.5-12.5 mm and counter punched with maximum limit of 16.5 mm.

When the centralizer is in operation, due to specially designed button which comprises of stainless steel or material with similar wear properties, integrated into the centralizer, fabricated on the first contact points or within highly deviated portion of centralizer having radially outward protrusion, act as the first point of contact on the centralizer and help to reduce the wear and abrasion of the centralizer, thereby reducing the co-efficient of friction and consequently reducing the torque.

As those with ordinary skill in the art will understand, various features illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative examples that are not explicitly illustrated and described. The combinations of features illustrated provide representative examples for typical centralizer. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those with ordinary skill in the art will recognize that the teachings of the present disclosure may be applied to other applications or implementations.

While the best mode has been described in detail, those familiar with the art will recognize various alternative designs within the scope of the following claims. 

I claim:
 1. A centralizer provided for lowering friction comprising: a plurality of collars including a first collar and a second collar; and a plurality of bow springs, each bow spring having a first end and a second end; wherein a plurality of buttons are mounted on said plurality of bow springs such that the first and second end of each bow spring is connected to the first and second collar respectively; the plurality of buttons are mounted on the bow springs such that at least one button from any plurality of bow springs is in contact with the borehole wall and act as the only/preferable point of contact between the centralizer and borehole; and said low friction buttons having low coefficient of friction than the rest of the body thus reducing torque and drag, thereby increasing the longevity of the centralizer.
 2. The centralizer as claimed in claim 1, wherein the low friction buttons are mounted on the bow springs such that they constitute the air gaps between borehole wall and the centralizer, thereby allowing said low friction buttons to touch on the borehole wall during run in the hole, providing minimum loss of the applied torque and high running force to the centralizer.
 3. The centralizer as claimed in claim 1, wherein said low friction buttons are composed of metal alloy.
 4. The centralizer as claimed in claim 3, wherein said metal alloy is preferably stainless steel.
 5. The centralizer as claimed in claim 1, wherein said centralizer is designed for open-hole and cased-hole logging applications.
 6. The centralizer as claimed in claim 1, wherein the coefficient of friction of said low friction buttons in water-based mud ranges from 0.10-0.15.
 7. The centralizer as claimed in claim 1, wherein the coefficient of friction of said low friction buttons in oil-based mud ranges from 0.05-0.10.
 8. The centralizer as claimed in claim 1, wherein the buttons are fitted in holes punched on centralizer.
 9. The centralizer as claimed in claim 8, wherein the holes are preferably oval with transverse diameter in range of 11-17 mm and longitudinal diameter in range of 13-15 mm. 